Whisk lemon juice, oil, garlic, oregano, salt and pepper in a small bowl. Reserve 2 tablespoons of this mixture for basting.

Drain and rinse tofu; pat dry. Cut the block crosswise into eight 1/2-inch-thick slices and place in a shallow glass dish. Add remaining marinade and turn to coat. Cover and refrigerate for at least 30 minutes or for up to 8 hours.